As a conventional art relating to a gland packing which is to be used in a shaft seal part of a fluid apparatus or the like, and a yarn used in the packing, known is a technique in which expanded graphite is used as a base material as disclosed in Japanese Patent Application Laying Open No. 63-1863 and Japanese Patent Publication No. 6-37546. This prior art discloses that a yarn for a gland packing is formed by filling the interior of a tubular member configured by braiding a fibrous material (knitting, hollow knitting, or the like), with a long expanded graphite sheet. A gland packing is produced by twisting or braiding using plural yarns which are thus produced (for example, eight-strand square braiding which uses eight yarns).
The conventional art which uses a thus configured yarn made of expanded graphite is conducted with the intention that, since the outer periphery of the expanded graphite base material is covered by knitting with a reinforcing material, or the like, the tubular member configured by braiding the reinforcing material counters a tensile or torsion force which is generated in each yarn when the gland packing is produced by braiding the plural yarns, and the expanded graphite base material in the tubular member is prevented from being broken.
As a manner of producing the yarn, as shown in Japanese Patent No. 2,562,603, only a concept of a production method or means that strip-like expanded graphite is introduced into a tubular member which is vertically directed, and a practical method of how to efficiently produce the yarn is not described.